Not so fast: Italian boffins say neutrinos not faster than light

Pistols at dawn at Hotel Gran Sasso?

A team of 68 scientists led by the Gran Sasso National Laboratory in Italy claims to have refuted the OPERA faster-than-light neutrino result, even as the OPERA researchers are generating a new buzz by releasing their newer, more-finely-calibrated short-pulse tests that seem to confirm their original statement.

Over the weekend, the OPERA team announced that its new neutrino experiment, which used much shorter pulses to try and remove a potential systematic error from the set-up. To make sure that they could prove the time correlation between the received neutrinos and the originating event, the latest test used pulses three nanoseconds long, with more than 500 nanoseconds between pulses.

Although only independent verification would constitute a “proof”, the new experiment still claims that the neutrinos arrived 57.8 ns (±7.8ns) too early.

However, the Gran Sasso group isn’t so sure. In this Arxiv paper, the ICARUS collaboration says it has refuted the faster-than-light result, based on an analysis of 2010 data from the ICARUS experiment which uses the same neutrino beam from CERN as OPERA.

Their claim is that in getting to superluminal velocities, the neutrinos should lose energy by producing photons and electron/anti-electron pairs (“e+e- pairs”), in a process “analogous to Cherenkov radiation” (the “blue glow” in nuclear reactor water, so beloved of movie-makers).

“A very significant deformation of the neutrino energy spectrum and an abundant production of photons and e+e- pairs should be observed,” the ICARUS group says.

This hasn’t happened, they assert: “We find that the neutrino energy distribution of the ICARUS events … agrees with the expectations for an undisturbed spectrum of the CERN neutrino beam.

“Our results therefore refute a superluminal interpretation of the OPERA result,” the group writes.

In other words, and if the ICARUS calculations are correct: the neutrinos should have lost a lot of energy getting to superluminal speeds; their spectrum seems to demonstrate that they didn’t lose that energy, therefore they can’t be passing the speed of light.

If there’s a better grand show than watching gold-standard peer-review play out in public, The Register would have trouble nominating what it could be. ®